Man unknown across the pond can take ecstasy (4,3)
I believe the answer is:
john doe
'man unknown across the pond' is the definition.
I can't judge whether this definition defines the answer.
'can take ecstasy' is the wordplay.
'can' becomes 'john' (slang for toilet).
'take' becomes 'do' (eg taking or doing drugs).
'ecstasy' becomes 'E' (informal term for the drug).
'john'+'do'+'e'='JOHN DOE'
Can you help me to learn more?
(Other definitions for john doe that I've seen before include "who's unknown" , "court's plaintiff imagined" .)